This section provides background information related to the present disclosure which is not necessarily prior art.
As is conventional, fluid pumps, such as gerotor pumps are used in power transfer units of the type installed in motor vehicles for supplying lubrication to the rotary driven components. Such power transfer units include manual and automatic transmissions, transaxles, and four-wheel drive transfer cases. Typically, a gerotor pump has a stationary outer ring defining a pumping chamber and an inner ring positioned in the pumping chamber and which is fixed for rotation with a driven member (i.e., a shaft, etc.). The inner ring has external lobes which are meshed with and eccentrically offset from internal lobes formed on the outer ring. Since the number of internal lobes is greater than the number of external lobes, driven rotation of the inner ring results in a pumping action wherein a supply of hydraulic fluid is drawn from a sump in the power transfer unit into the suction side of the pumping chamber and is discharged from the pressure side of the pumping chamber at an increased pressure.
A drawback associated with conventional gerotor pumps is that the pumping action is only generated in response to rotation of the inner ring in one direction. As such, gerotor pumps are arranged in most power transfer units to generate the pumping action during rotation of the inner ring in a direction corresponding to forward driven operation of the motor vehicle. Since the gerotor pump does not generate a supply of hydraulic fluid when the inner ring is driven in the opposite direction, an undesirable condition may result wherein an inadequate supply of lubrication is delivered to the rotary components during extended periods of reverse operation. To alleviate this condition, some power transfer units are equipped with a first pump for lubricant supply in forward operation and a second pump for lubricant supply in reverse operation. As is obvious, the addition of a second pump adds both cost and weight to the power transfer unit. Thus, a continuing need exists to develop alternatives to conventional uni-directional gerotor pumps for use in power transfer cases.
To secure these gerotor pumps to the rear transfer case housing, the pump housing typically includes radial tabs formed around an outer periphery thereof, which are configured to engage pockets or keyways in the power transfer case housing to allow the pump to be firmly secured therein. These components are formed such that when the pump housing is installed in the rear transfer case housing, a nominal clearance exists between the radial tabs on the pump housing and the pockets formed in the transfer case housing. This clearance is intended to allow for blind installation of the rear housing over the pump. It is known that this nominal clearance can create undesirable noise issues in some vehicles, which results from the pump tab hitting the rear housing during vehicle operation. Eliminating this potential for noise would thus be highly desirable.